Pipe runs for sewage systems and the like are terminated at predetermined intervals within manhole assemblies to facilitate maintenance, inspection and repair. A coupling seal is provided between the manhole opening and the pipe to provide a watertight seal therebetween and preferably to allow for some movement of the pipe relative to the manhole assembly, typically caused by external forces.
One technique for accomplishing this type of seal is described in U.S. Pat. Nos. 3,796,406; 3,813,107 and 3,832,438 and assigned to the assignee of the present invention. This technique employs a gasket which has its outer periphery embedded in the concrete material during the time that the manhole member is cast. Although this type of gasket provides a good watertight seal between the manhole opening and the pipe, the amount of movement which the pipe can experience relative to the manhole opening is quite limited, due to the nature of the gasket.
The misalignment of a pipe relative to the manhole opening may be significant in certain applications and further since the pipe may undergo a significant amount of movement relative to the manhole as a result of subterranean influences, a gasket has been developed to accomodate significant changes in the displacement between the pipe and the manhole opening which gasket and method of assembly is described in U.S. Pat. No. 4,103,901, issued Aug. 1, 1978 and assigned to the assignee of the present invention. The gasket disclosed in the last mentioned patent is comprised of an outer peripheral flange which is embedded in the concrete material from which the manhole assembly is cast. The gasket is provided with a central opening defined by a gasket inner annular periphery shaped to have an appearance substantially similar to an O-ring, said gasket further including an integral, intermediate section having first and second diagonally aligned portions integrally joined at opposite ends to said outer flange and said inner periphery and integrally joined to one another along an imaginary circular line defining a V-shape with the fold being at the point joining the aforesaid portions. The gasket is arranged within the manhole opening such that the outer flange is embedded in the concrete surrounding said opening. The O-ring shaped inner periphery is sufficiently yieldable to embrace the outer surface of a pipe section extending therethrough. The intermediate section of the gasket is V-shaped to enable the gasket to resiliently support a pipe, ideally so that its longitudinal axis coincides with the axis of the manhole opening and yet which is sufficiently and readily yieldable to resiliently support the pipe relative to the manhole member and retain the watertight seal therebetween in spite of the fact that the pipe undergoes a significant displacement from the aforementioned concentric position with the manhole opening. This displacement may be of the order of several inches.
Although the above described gasket has the capability of accommodating pipes having an outer diameter which deviates from a nominal value over a significant range which is of the order of several inches and is further capable of maintaining a watertight seal between the pipe and the manhole opening in spite of an alignment displacement therebetween of the order of several inches, the above described gasket is designed to be embedded into the manhole base at the time that the base member is cast.